1. Field of the Invention
This invention relates to scanners for providing electronic signals descriptive of information in a document.
2. Description Relative to the Prior Art
U.S. Pat. No. 4,568,984 discloses method and apparatus for scanning rasters to generate simultaneously opaque and transparency signals of each point of the raster. Line scanning is effected with a light source directed at a polygon with the beam deflected by the polygon being passed through a lens and directed at the document. Light reflected by the document is integrated in an integrated cylinder and collected to a sensor. When scanning a raster, for the signals derived from the sensor to have useful meaning, it must be known accurately what is the actual location of the scan line to which the instantaneous signal relates. In U.S. Pat. No. 4,568,984, because the document is flat and the scanning beam is scanned at constant angular velocity, a f.theta. lens is needed if the linear velocity of the point of incidence of the beam on the document is to be linearly related to the angular velocity of the polygon. If the beam is convergent on the document, then the lens also has to exhibit a focal length which varies with the inclination of the incident beam, if the beam is always to be held in focus on the flat document and thereby give a spot with a diameter which is uniform whatever the position along the scan line.
A lens which has the above-described capabilities is complex and expensive.